Referring to FIG. 1, an example of a transfer case 7 is shown. The transfer case 7 has a housing 10. The housing 10 has a front cover plate 12 that is boltably connected to a main body 14. Rotatably mounted within the transfer case housing 10 is an output or primary shaft 16. The primary shaft 16 has a front end that can be selectively torsionally connected with an input shaft 17. Input shaft 17 is connected with an output shaft (not shown) of a transmission of the vehicle. Typically, the vehicle is a rear wheel drive vehicle with a longitudinally mounted engine. The drive train for the vehicle is configured in such a way that power can be selectively diverted from a rear axle to be shared with a front axle to provide the vehicle with all wheel drive capability. The primary shaft 16 is mounted within the front cover plate 12 by needle bearings 20 within an axial bore of the input shaft 17. A rearward portion of the primary axle 16 is rotatably mounted within the housing main body 14 by a rear bearing 22. A rear end of the primary shaft (not shown) is connected with a yoke (not shown) that is connected with a drive line extending to a vehicle rear differential and axle (not shown).
At a lower elevation, the transfer case 7 also rotatably mounts a secondary shaft 34. The secondary shaft 34 is configured to power either directly or via a universal type joint, a front drive line shaft (not shown) that is torsionally connected with a differential for the front wheels of the vehicle. In another embodiment (not shown), the secondary shaft 34 can be connected with a front wheel drive line via a flange connection. An exterior of the secondary shaft is connected with a sprocket 38. The sprocket 38 engages a flexible torsional force transfer member or a belt (shown schematically) which is typically provided by a multi-link chain 40. The chain 40 is engaged with a primary sprocket 44. The primary sprocket 44 is rotatably mounted on the primary shaft 16.
To allow the primary shaft 16 to selectively torsionally engage the secondary shaft 34, there is provided an electromagnetic clutch 50. The clutch 50 has a housing 52 that is spline connected to the primary shaft 16. The housing 52 has annular cup 53 formed about an annular shape electromagnet 56. When actuated the electromagnet 56 attracts a clutch plate 58 to make contact therewith. Clutch plate 58 pulls back a housing 60 that is axially spline connected to the primary sprocket 44. Clutch plates 58 connection with annular cup 52 torsionally connects the primary sprocket 44 with the shaft 16 allowing the primary shaft 16 to selectively power the secondary sprocket 38 and its associated secondary shaft 34.
Transfer case 7 also has a hub 70. Hub 70 on its outer diameter has a stub gear 72. Stub gear 72 is spline connected to an inner diameter bore of the input shaft 17 (in stub gear's 72 forward position). Input shaft 17 on its outer diameter has an integrally formed sun gear 74. Sun gear 74 engages with a planet gear 76 that in turn spins about a carrier pin 78. Planet gear 76 also engages with a ring gear 80 that is fixed within the transfer house front plate 12. Hub 70 along its inner diameter is spline connected to the primary shaft 16. Hub 70's position shown in FIG. 1 torsionally connects the primary shaft 16 with the input shaft 17 for high gear range operation for either four wheel or two wheel drive operation dependent upon the position of clutch 50. When a low gear range operation is desired, a shift fork 82 moves hub 70 (rearward) causing the stub gear 72 of the hub 70 to engage with inner diameter gear 86 provided by carrier plate 88 which is fixedly connected with carrier pins 78. Stub gear 72 is now torsionally connected with carrier plate inner diameter gear 86 and power from input shaft 17 flows through its integral sun gear 74, planet gear 76, in a reduced gear ratio causing movement of carrier pins 78 in the same direction of the input shaft. Power is then delivered through carrier gear 86 into the stub gear 72 into the output shaft 16. If a neutral output is desired the shift fork positions the hub 70 in a position that its stub gear 72 proximately in a space 90 that is not engaging either the input shaft 17 or with the carrier gear 86 thereby essentially disengaging the primary shaft 16 from input shaft 17. Positioned generally rearward of the shift fork 82 and forward of the primary sprocket is a gear rotor type oil pump 92. As apparent to one skilled in the art, when transfer case 7 is in a high gear operating as shown in FIG. 1, there is still engagement between the sun gear 74 the input shaft 17 causing parasitic loss by its engagement of planet gears 72 of planetary gear set. It is desirable to provide a transfer case wherein the transfer case can have a high gear mode and a low gear mode wherein the low gear mode is provided by planetary gear system wherein when the transfer case is in a high gear mode of operation the planetary gear set is not engaged.
Many vehicles with transfer cases with high and low gear outputs are utilized in off road type SUV's and pickup trucks. It is often desirable to be able to tow SUV's or pickup trucks on all four wheels, especially when towing over long distances. To accommodate long distance towing on all four wheels, many transfer cases in combination of high and low gear settings also have a neutral setting. When the transfer case is in a neutral setting the transmission of the vehicle is torsionally isolated from the front and rear axles. If the transmission is isolated from both the front and rear axles, the vehicle can be towed on all four wheels without rotation of the transmission. The transmission is not damaged due to rotation without being supplied with lubricant from the transmission oil pump (typically powered by the vehicle engine, which is turned off during long distance towing). However, when the transfer case is in neutral, and the transmission is in park, the vehicle is free to roll forwards or backwards. Therefore, it is very important that the operator of the vehicle be cognizant of the fact when the transfer case is in the neutral position. To inform the vehicle operator that the transfer case is in the neutral position, the transfer case is reliant upon positional sensors. Due to dimensional tolerances and spring compliance of assembled components, it can be difficult for a sensor to determine if the transfer case is in high gear, low hear or neutral. Therefore, it is highly desirable that the neutral position be at an extreme position of the shift fork so that when the transfer case is in a neutral position, the determination of the transfer case status can be clearly determined. Therefore, it is also desirable that the shift from low gear to high gear mode of operation of the transfer case be immediate without a neutral position between the low gear mode of operation and a high gear mode of operation. Accordingly, the neutral position of the transfer case shift fork should be an extreme position.